2021 NJC Prelim P1 Ans

1 8873/01 [Turn over NATIONAL JUNIOR COLLEGE SH 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Multiple Choice Answer Sheet Data Booklet 8873/01 Wednesday 15 September 2021 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, subject class and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Instructions on how to fill in the Optical Mark Sheet Shade the index number in a 5 digit format on the optical mark sheet: 1st digit and the last 4 digits of the Registration Number. Example: Student Examples of Registration No. Shade: 2005648 25648 This document consists of 12 printed pages.

2 8873/01 [Turn over 1 Which statement about 1 mol of a metal is always true? 1. It has the same number of atoms as 1 mol of hydrogen atoms. 2. It loses 1 mol of electrons. 3. It contains half the number of atoms as 2 mol of HCl(g). 4. It contains 1 3 the number of ions as 3 mol of Na2O(s). A 1 B 1 and 3 C 1, 2 and 3 D 1, 3 and 4 1: Correct. 2: Incorrect. Different metals liberate different moles of electrons. Eg 1 mol of Mg is liberated by 2 mol of electrons. 1 mol of Na is liberated by 1 mol of electrons. 3: Incorrect. 2 mole of HCl(g) contain 4 moles of atoms. 4: Incorrect. 1 mole of Na2O contain 3 moles of ions. For 1/3 of 3 moles of Na2O, there are 3 moles of ions. Answer: A 2 The actual values of the masses of three sub-atomic particles are shown in the table. proton neutron electron mass/kg 1.673  1027 1.675  1027 9.109  1031 Which nickel ion is predicted to have a mass of 1.038  1025 kg from these data? A 𝑁𝑖28 60 2+ B 𝑁𝑖28 62 2+ C 𝑁𝑖28 58 3+ D 𝑁𝑖28 64 3+ No. of protons No. of neutrons No. of electrons 𝑁𝑖28 60 2+ 28 60 – 28 = 32 28 – 2 = 26 𝑁𝑖28 62 2+ 28 62 – 28 = 34 28 – 2 = 26 𝑁𝑖28 58 3+ 28 58 – 28 = 30 28 – 3 = 25 𝑁𝑖28 64 3+ 28 64 – 28 = 36 28 – 3 =25 Mass = 28(1.673  1027) + 34(1.675  1027) + 26(9.109  1031) = 1.038  1025 kg Answer: B

3 8873/01 [Turn over 3 The redox half-equations for the electrolysis of dilute sodium chloride solution are stated below. Oxidation half-equation: 2H2O → O2 + 4H+ + 4eˉ Reduction half-equation: 2H2O + 2eˉ → H2 + 2OHˉ Which row shows the correct volume of gases if 2.40 mol of electrons are involved in the redox reaction? Volume of H2 gas collected at r.t.p / dm3 Volume of O2 gas collected at r.t.p / dm3 A 28.8 14.4 B 28.8 28.8 C 14.4 7.2 D 14.4 28.8 Mole ratio: O2 : e : H2 1 : 4 : 2 Amount of H2 = 2.4 4  2 = 1.2 mol Vol of O2 collected = 1.2  24 = 28.8 dm3 Amount of O2 = 2.4 4 = 0.6 mol Vol of O2 collected = 0.6  24 = 14.4 dm3 Answer: A

4 8873/01 [Turn over 4 Use of the Data Booklet is relevant to this question. To identify a compound, the compound can be broken down into ions and passed through an electric field. In this electric field, the 4He nucleus is deflected +8o and used as a standard. An unknown ionic compound was broken down and passed through the same electric field. Two monocharged fragments were observed to have deflected +0.6o and −0.45o. What could be the ionic compound? A LiCl B LiBr C NaCl D NaBr angle of deflection α mass sizeeargch for 4He2+, 8 =k +2 4 , k = 16 For a deflection of +0.6, 0.6 =16 × 1 𝑥 , x = 23 For a deflection of −0.45, 0.45 =16 × 1 𝑥 , x = 35.5 Compound is NaCl Answer: C 5 10 cm3 of propane, C3H8, was completely burnt in x cm3 of excess oxygen. After cooling to room temperature, the volume of the residual gas was 60 cm3. The residual gas was passed through aqueous sodium hydroxide and the volume reduced to y cm3. What are the values of x and y? x y A 50 30 B 60 30 C 70 20 D 80 30 C3H8 + 5O2  3CO2 + 4H2O 10 cm3 requires 50 cm3 of oxygen for complete combustion and 30 cm3 of CO2 will be produced. y = volume of unreacted oxygen = 60-30 = 30 cm3 Hence x = 50 + 30 = 80 cm3. Answer: D

5 8873/01 [Turn over 6 Propyne, C3H4, has the following structure. Which option correctly describes the number of σ and π bonds present in a molecule of propyne? σ π A 2 2 B 2 6 C 1 3 D 6 2 All single bonds are sigma bonds. A triple bond has one sigma bond and two pi bonds. Total of 6 sigma and 2 pi bonds. Answer: D

6 8873/01 [Turn over 7 Which statement is true for all covalent bonds? A A covalent bond cannot be found in ionic compounds. B A covalent bond can be formed via head-on overlap of p orbitals. C A covalent bond can only be formed between two non-metal atoms. D A covalent bond is formed when each bonding atom contributes a valence electron. A: incorrect. Polyatomic ions, such as sulfate ions (SO42‒), consists of covalent bonds between the S and O atoms. B: correct. Fluorine is an example where the covalent bonds are formed via head -on overlap of p orbitals. C: incorrect. Aluminium chloride is an example of a molecule with covalent bonds between metals and non-metals. D: incorrect. A dative covalent bond is formed when the shared pair of electrons is provided by only one of the bonding atoms. Answer: B 8 Which conditions would result in the most significant intermolecular forces between gaseous oxygen molecules? pressure temperature A high low B High high C low high D low low High pressure: oxygen molecules are closer together Low temperature: oxygen molecules has lower kinetics energy, which will cause oxygen molecules to be closer together. Answer: A

7 8873/01 [Turn over 9 Which statements can be explained in terms of hydrogen bonding? 1 The apparent relative molecular mass of ethanoic acid in benzene is 120. 2 HF2‒ is formed when HF is dissolved in molten NaF. 3 The boiling point of propanoic acid is higher than ethanoic acid. 4 Ice is less dense than water. A 1, 2 and 3 B 2, 3 and 4 C 1, 2 and 4 D 1 and 4 Propanoic acid has higher bp than ethanoic acid due to the larger electron cloud size of the molecule which will imply that it has stronger instantaneous dipole – induced dipole interactions. Answer: C 10 Which species is not planar? A BrF3 B ICl4 C PCl4+ D XeF4 A: BrF3 : T–shaped (3 bp, 2 lp) B: ICl4– : square planar (4 bp, 2 lp) C: PCl4+: tetrahedral (4 bp, 0 lp) D: XeF4: square planar (4bp, 2 lp) Answer: C

8 8873/01 [Turn over 11 Which statements are correct for all systems at dynamic equilibrium? 1 It is a closed system. 2 The rate of both forward and backward reactions is the same. 3 The concentration of reactants is equal to the concentration of products. A 1 and 2 only B 1 and 3 only C 2 and 3 only D 2 only 12 Nitrosyl chloride, NOCl, is a yellow gas that can be formed between nitryl chloride, NO 2Cl, and nitric oxide, NO, in the following reaction. NO2Cl(g) + NO(g) ⇌ NOCl(g) + NO2(g) ∆H < 0 NO2Cl and NO were initially allowed to react in a closed vessel at 800 K and equilibrium was established. The graph below shows how the concentration of NO2Cl varied with time. What could be the changes made to the system at